Ion beam definition of magnetoresistive field sensors

ABSTRACT

A magnetoresistive (MR) sensor can be shaped using ion beam irradiation and/or implantation through a mask introduced between a MR structure and an ion source. The mask covers selected portions of the MR structure to define the track width of the sensor. Ion irradiation and/or implantation reduces the magnetoresistance of the unmasked portions while leaving the masked portion substantially unaltered. The mask can be a photoresist mask, an electron beam resist mask, or a stencil mask. Alternatively the mask may be part of a projection ion beam system. Track width resolution is determined at the mask production step. The edges of the sensor can be defined by a highly collimated ion beam producing an extremely straight transition edge, which reduces sensor noise and improves sensor track width control. Improved hard bias layers that directly abut the sensor may be used to achieve a suitable stability. A variety of longitudinal bias schemes are compatible with ion beam patterning.

This application is DIV of Ser. No. 09/669,080 filed Sep. 25, 2000, nowU.S. Pat. No. 6,741,429.

FIELD OF THE INVENTION

This invention relates generally to forming magnetoresistive fieldsensors. More particularly, this invention relates to magnetic recordingsystems.

BACKGROUND ART

Sensors for detecting and measuring magnetic fields find many scientificand industrial applications. For example, a magnetic recording headtypically includes a sensing element that senses a magnetic fluxemanating from a recording medium. The magnetic field changes somephysical property of the sensing element in a manner that depends on themagnitude and direction of the magnetic field. A sensing element thatchanges its electrical resistivity in response to a magnetic field isusually referred to as a magnetoresistive field sensor. Priormagnetoresistive field sensors typically include one or moreferromagnetic elements whose resistivity changes in response to magneticflux. Prior magnetoresistive field sensors include anisotropicmagnetoresistive (AMR) sensors and giant magnetoresistive (GMR) sensors,in which a sense current flows along, or perpendicular to, planes of theferromagnetic elements. Prior magnetoresistive field sensors alsoinclude magnetoresistive tunnel junction (MTJ) sensors, in which a sensecurrent flows perpendicular to the planes of the ferromagnetic elementsthrough a dielectric barrier. Resistance of a magnetoresistive fieldsensor varies as the square of the cosine of the angle between themagnetization in the sensor and the direction of sense current. Recordeddata can be read from a magnetic medium because the external magneticfield from the recorded magnetic medium (the signal field) causes achange in the direction of magnetization in the sensor, which in turncauses a change in resistance in the sensor and a corresponding changein the sense current or voltage.

Increasing areal density of magnetic storage media requires that themagnetic recording and reading heads be able to operate atever-decreasing track widths (TW). Both the write element and themagnetic readback sensor of the recording head must be made smaller inorder to achieve narrower data tracks. The width of the recorded trackis determined by, among other parameters, the width of the write pole ofthe write head and the flying height of the write head. The size andgeometry of the shields and leads also play a role in determiningachievable track width for a given recording head design.

In order to take advantage of the narrower write track width, it isimperative that the read track width of the readback element or readhead be reduced as well. At present, magnetoresistive (MR) heads aretypically made by photolithographically defining the sensor element froma continuous multilayer thin film. The sensor, which is frequentlyrectangular in shape, is often defined in two steps, onephotolithographic step to define the TW dimension, and one lapping stepto define the so-called “stripe height” (SH) dimension. Unfortunately,due to practical limitations of the lithographic method, such as thediffraction limit of light, it is not easy in a manufacturingenvironment to produce read heads much narrower than about 200 nm.Meanwhile, MR head technology is already pushing presentphotolithographic techniques to their limits and these present methodswill not be able to accommodate future generations of MR heads. Forexample, in current commercial products, the sensor TW, which is definedby optical lithography and ion beam milling, is typically less than 1μm. It is envisaged that in order to make heads suitable for recordingdensities of 100 Gbits/in², the sensor TW will need to be around 0.13μm, but current lithography is wavelength-limited to around 0.2 μm.

An associated problem that arises from the current processing method ispoor shape definition, which leads to a “tail” on each side of thesensor. The tails are a result of the ion beam milling process commonlyused to define TW. The milling is performed with the ion beam at anangle to the wafer in an effort to minimize the redeposition of magneticmaterial at the mask edges, which would have a deleterious effect on thesensor performance. However, ion milling at an angle creates a shadownear the mask edges, within which the milling is less efficient,resulting in tails on the sensor structure. The beam divergence from theion mill also contributes to the tails. The presence of the tailsdegrades the magnetic performance of the sensor. Further, the tails mayvary in dimension and form across the wafer, resulting insensor-to-sensor variation in performance. FIG. 1 illustrates across-sectional schematic diagram of a contiguous junction design MRsensor 100. MR sensor 100 includes a first magnetic shield 102, and afirst insulating gap 104 disposed on the shield 102. The sensing element106 including tails 108 is disposed on the gap 104. Following themilling process, the top of the multilayer sensing element 106 will havea width determined by the resist mask used. However, the all-importantsense layer, which is located further down in the multilayer stack thatforms sensing element 106, will inevitably have a larger and possiblynot well-controlled width. This problem is predicted to becomeincreasingly important as the TW decreases and the tails becomeproportionally larger relative to the sensor dimensions.

Once the sensing element 106 is formed using optical lithography andmilling, it is usual to deposit a ferromagnetic layer, called “hardbias” layer 110, with substantial magnetic coercivity (Hc) on each sideof the sensing element 106 to stabilize the magnetization at each sideof the sensing element, thereby improving sensor performance. However,the tails 108 on each side of the sensing element 106 make deposition ofa uniform hard bias layer 110 difficult, and the hard bias layer 110becomes very thin near the top surface of the sensing element 106 and/ordoes not closely abut the sensing element 106, leading to poor sensorperformance.

MR sensor 100 further includes leads 112 adjacent to hard bias layers110 to conduct the sense current to the sensing element 106 when readingdata stored on a magnetic recording medium, a second gap 114 and asecond shield 115 to protect the sensing element 106.

A U.S. patent application entitled “Track Width Control of ReadbackElement” field Jun. 30, 1999, to Patrick C. Arnett et al. discloses amethod for reducing the track width of readback elements by implantationof ions. The ion implantation reduces the magnetoresistance of theselected portions of the readback elements. The ion implantation ofArnett et al. is performed by a focused ion beam (FIB) technique.However, FIB processing is slow, since each element is processed inseries, which is not desirable for mass manufacture of magnetic sensors.Furthermore, electrostatic discharge (ESD) damage can occur during theapplication of the FIB to the sensor element, and therefore groundingduring processing and low ion currents will be required to minimize thisrisk. In addition, the FIB processing of Arnett et al. is performed fromthe air-bearing surface (ABS). The layers that make up the sensortypically run perpendicular to the ABS and have stripe heights about anorder of magnitude or more greater than the sensor film thickness.Consequently the ions must penetrate to a greater depth than the sensorfilm thickness in order to define the magnetically sensitive “tipportion”. A large depth requirement demands high ion energies(incidentally, well beyond the range of standard FIB machines). Theincreased ion energy will cause an increase in the lateral straggle ofthe ions in the sensor material, and will widen the transition regionbetween the tip portion and the neighboring “magnetically deactivated”region, presumably degrading the performance of the sensor. In order toconduct “implantation” amounting to a typical few atomic percent of thecritical layers, this technique requires extremely large ion doses withlong processing times, resulting in problems with heat dissipation andsurface sputtering. Furthermore, this technique teaches an implantationbased on a geometry which is quite unlike that used in recording headsor other MR sensors.

An article entitled “Patterning Ferromagnetism in Ni₈₀Fe₂₀ Films via 30keV Ga⁺ Ion Irradiation” submitted to Applied Physics Letters on Mar.30, 2000 by W. M. Kaminsky et al. discloses a method to degrade and evendestroy the ferromagnetism of a GMR multilayer system, such asNi₈₀Fe₂₀/Cu/Ni₈₀Fe₂₀/Ni₈₀Cr₂₀, by exposing this GMR multilayer system tohomogeneous 30 keV Ga⁺ implantation. Ga⁺ implantation destroys allappearances of ferromagnetism at room temperature. The degradation offerromagnetism occurs primarily because of ion implantation. Kaminsky etal. describe FIB irradiation of a single layer film to fashion alaterally patterned multilayer system. Such an approach would work forpatterning the film from the ABS level to produce a read-back sensor.However, this is impractical for mass production of magnetic sensors forthe reasons discussed above. Additionally, the lateral scattering of theimplanted ions in the material is too great to produce implanted regionssufficiently narrow, and with sufficiently perfect interfaces, to allowa magnetoresistive sensor to be produced which would produce signalscompetitive with those from thin film sensors.

U.S. Pat. No. 5,079,662 issued on Jan. 7, 1992 to Kawakami et al.discloses a compound magnetic head in which the read element issandwiched between the poles of the write gap. This patent has mentionedthe ion implantation into selected areas of recording heads. However,the ion implantation is performed to increase the coercive field inthose areas.

There is a need, therefore, for a MR recording head having improveddefinition of patterned magnetic sensors and a method of fabricatingsame.

OBJECTS AND ADVANTAGES

Accordingly, it is a primary object of the present invention to providea MR sensor with improved shape definition.

It is a further object of the invention to provide a MR sensor withcontrolled track width.

It is a further object of the invention to provide a MR sensor withwell-controlled biasing for magnetic stabilization.

It is an additional object of the invention to provide a method forfabricating such a MR sensor.

SUMMARY

These objects and advantages are attained by MR sensors with small trackwidths defined using ion irradiation and/or implantation at the waferlevel.

According to a first embodiment of the present invention, a MR structurehas a sensor defined by ion irradiation and/or implantation through amask introduced between the film and the ion source at the wafer level.The unmasked portions of the MR structure are irradiated or implantedwith ions, which reduces the magnetoresistance of the unmasked portions.However, materials of the unmasked ion-treated portions are stillelectrically conductive, which may be used as the lead, or part of thelead structure. Irradiation, as used herein, is distinguished fromimplantation in that ions irradiating a layer of material havesufficient energy to pass through the layer without being embedded inthe layer. Furthermore, the irradiating ions have sufficient energy thatthey pass through the layer without significant sputtering or milling ofthe layer.

The mask may be a photolithographic resist mask located in contact withthe surface of the magnetoresistive (MR) structure to cover selectedportions of the MR structure and it is sufficiently thick to stop theions incident on those regions, preventing them from reaching the MRstructure. The unmasked portions are exposed to ion beams for patterningthe sensor and reducing the magnetoresistance of the unmasked portionswhile leaving the masked portions, which define the track widths,magnetoresistive. Alternatively, an electron beam resist mask may beused. A designed TW may be achieved depending on the size of the resistmask used in irradiation and/or implantation process. Fabrication of aMR sensor using a resist mask allows for track width as small as 5 nm.

As an alternative to a resist mask, a stencil mask may be suspendedabove the surface of a MR structure during ion irradiation and/orimplantation. The stencil mask may be produced using photolithography,electron-beam lithography, or other appropriate techniques. By choosingsuitable ions and energies to minimize sputtering, the stencil mask maybe used repeatedly, thus the cost of producing the mask is of smallimportance to manufacturing.

Alternatively, the sensor of a MR structure may be defined by ionirradiation and/or implantation using a projection ion beam system. Inthe projection ion beam system, a collimated ion beam is projectedthrough a mask, which is disposed between the MR structure and an ionsource. The ion beam is focused by beam optics after passing through themask. A design TW may be achieved depending on the distance between themask and the surface of the MR structure, the properties of the beamoptics, and the size of features in the mask.

According to a second embodiment of the present invention, themagnetization of defined sensors of the types as described in the firstembodiment may be stabilized by using a hard bias layer adjacent to thesensor. Alternatively, the magnetization of the defined sensor may bestabilized by using an anti-parallel (AP) pinning layer or an in-stackanti-ferromagnetic (AF) layer.

The methods of using ion implantation/irradiation for reducing themagnetoresistance and magnetic moment of the unmasked portions describedin the first embodiment may be used for AMR, GMR and MTJ sensors. Themagnetoresistance of a typical NiMn-based multilayer MR structure fallsto around 3% of the as-grown value with an ion dose of 10¹⁶ ions/cm².However, although the ion irradiation reduces the magnetoresistance ofthe unmasked portions, the magnetic moment of those portions is notsubstantially altered. Ion implantation with suitable species reducesthe magnetic moment and the magnetoresistance of the unmasked portionsto zero. The magnetoresistance of typical spin valve samples dropsrapidly from around 10% to near zero with increasing dose of implantedions. The total moment of the films drops to zero after about fourmonolayers equivalent coverage of ions (about 2×10¹⁶ ions/cm²).

MR heads having defined sensors of the types as described in the firstand second embodiments may be incorporated into a disk drive accordingto a third embodiment of the present invention. The disk drive includesa magnetic recording medium, a MR head with a defined sensor, anactuator connected to the MR head for moving the MR head across themagnetic recording disk, and a mechanism for moving the disk relative tothe MR head.

MR sensors and disk drives made according to the various embodiments ofthe present invention exhibit edge definitions with narrow track widthssuitable for future high density magnetic recording products.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a schematic diagram of a MR structure according to theprior art;

FIG. 2 depicts a schematic diagram of a fabrication of a MR structureaccording to a first embodiment of the present invention;

FIG. 3A depicts a schematic diagram of fabrication of a MR structure inwhich an ion beam mill step is used in addition to an ionirradiation/implantation step according to an alternative embodiment ofthe present invention;

FIG. 3B depicts a schematic diagram of fabrication of a MR structure inwhich one mask is used in conjunction with an ion mill step to grosslydefine the sensing element and a second, smaller mask is used to definethe TW via ion irradiation/implantation according to an alternativeembodiment of the present invention;

FIG. 3C depicts a schematic diagram of fabrication of MR sensors usingan ion beam projection system according to an alternative embodiment ofthe present invention;

FIG. 4A depicts a plot showing the effect of irradiation with 700 keV N⁺ions on the normalized magnetoresistance (ΔR/R) of a NiMn-basedmultilayer;

FIG. 4B depicts a plot showing the effect of implantation on thenormalized magnetic moment of a multilayer MR structure;

FIGS. 5A-5E depict schematic diagrams of sensor stabilization accordingto a second embodiment of the present invention; and

FIG. 6 depicts a schematic diagram of a disk drive according to a thirdembodiment of the invention.

DETAILED DESCRIPTION

Although the following detailed description contains many specifics forthe purposes of illustration, anyone of ordinary skill in the art willappreciate that many variations and alterations to the following detailsare within the scope of the invention. Accordingly, the followingpreferred embodiment of the invention is set forth without any loss ofgenerality to, and without imposing limitations upon, the claimedinvention.

FIG. 2 depicts a cross-sectional schematic diagram of fabrication of aMR structure 200 according to a first embodiment of the presentinvention. MR structure 200 includes a thin film of magnetoresistive(MR) material, which includes portions 206 and 208, disposed on asubstrate 204 which may include an insulating gap layer and/or amagnetic shield layer. A mask 210 covers the portion 206, which is adefined sensor of MR structure 200. The unmasked portions 208 areexposed to the ions 212. The ions irradiate and/or implant into theunmasked portions 208 and reduce the magnetoresistance of these portionswhile leaving the masked portion 206 substantially unaltered. However,the unmasked portions 208 are still electrically conducting, which maybe used as the lead, or as part of the lead structure. This technique ispreferred for implantation since the ion-treated material may benon-magnetic, which may minimize side-reading effects.

The mask may be made of a resist deposited on the surface of a MRstructure as shown in FIG. 3A. The resist may be patterned using opticalor electron-beam lithography. Alternatively, a stencil mask may be used.Stencil masks can be made from Si or any other suitable material, by anyconvenient technique, such as optical lithography, electron beamlithography, focused ion beam lithography, or projection ion beamlithography. With a suitable mask it would also be possible to make thesensor shown in FIG. 2 using projection ion beam lithography, whereinthe ion beam is focused after passing through the mask. This approachoffers the advantage that the patterns in the mask can be considerablylarger than the patterns projected on to the MR film which define thesensor structure. FIG. 3A illustrates a cross-sectional schematicdiagram of fabrication of a MR sensor 300 with a mask 311 for patterningand irradiation/implantation with ions according to an alternativeembodiment of the present invention. MR sensor 300 includes a MRstructure containing a defined sensing element 301 and tails 303, whichare disposed on a substrate 304. The mask 311 covers a selected portionof the MR structure to define the sensing element 301. The combinedstructure of the defined sensing element 301 and tails 303 has beenproduced by ion milling in conjunction with the mask 311. The unmaskedportions of the MR structure, e.g., the tails 303, are exposed to theions 312. The ions 312 irradiate and/or implant into the unmaskedportions 303 and reduce the magnetoresistance of these portions whileleaving the masked portion 301 substantially unaltered. The irradiationand/or implantation does not affect the magnetization of the maskedportion 301, thus the sensor is defined. A design TW of the sensingelement 301 may be achieved depending on the size of the mask 311.

FIG. 3B illustrates an alternative process for defining a sensor inwhich the sensing structure is grossly defined in a first step using amask which is subsequently removed. In a second step, illustrated here,a smaller mask is used in conjunction with ion irradiation/implantationto destroy the MR in the tails of the sensing structure, thus definingthe TW dimension. As shown in FIG. 3B, MR sensor 302 includes sensingelement 306 and tails 308, disposed on substrate 305, which are producedfrom a continuous thin MR film using a conventional ion beam millingprocess in conjunction with a first mask (not shown here). Alternativemilling or etching processes could be used at this step. A second mask310 is inserted between the MR sensor 302 and a source of ions 312.Unmasked portions such as the tails 308 are exposed to the ions 312. Theions irradiate or implant into the unmasked portions thereby reducingthe magnetoresistance of the unmasked portions. The reducedmagnetoresistance, e.g., in the tails 308, defines the TW edge of thesensing element 306. A designed TW of sensing element 306 is achieveddepending on the size of the mask 310.

Alternatively, a sensor with tails resulting from a conventional ionmilling process of a MR sensor may be further defined with a projectionion beam system, as shown in FIG. 3C. In FIG. 3C, a MR sensor 332includes a MR structure containing a defined sensing element 315 andtails 317, which are disposed on a substrate 304. A rigid mask 314 madefrom Si or any other suitable materials is suspended between the MRstructure and a source of a collimated beam of ions 312. Portions of themask 314 block the ions from striking one or more selected portions 315of the MR structure. Ion optics 316 focus the ions 312 onto unmaskedportions 317 of the sensor 332. The beam of ions 312 projects onto theunmasked portions 317. Ion irradiation and/or implantation of theunmasked portions 317 reduces the magnetoresistance of the unmaskedportions 317 and, thus, defines the sensing element 315. A designed TWof the sensing element 315 may be achieved depending on a distancebetween the mask 314 and the surface of the MR sensor 332, theproperties of the ion optics, e.g., focal length, and the size offeatures in the mask 314.

The technique of using ion irradiation and/or implantation to define theTW as described in FIGS. 2 and 3A-3C may be used for fabricating GMRsensors, such as spin valves, MTJ sensors, or any magnetic multi-layersensor structure. These processes use a broad collimated ion beam andmasks to perform TW definition and allow TW definition of all the sensorelements on a wafer simultaneously, maximizing the manufacturingthroughput and minimizing cost. Since the ion beam may be applied to acontinuous film at the wafer level, the electrostatic discharge (ESD)problem is circumvented. In addition, the ions impinge on the sensor inthe direction normal to the magnetic layers of the unmasked portions,and need only penetrate a short distance to do the requisite damage tothose layers. Therefore, the ion energy required is low, minimizingmilling during irradiation/implantation, thus maintaining a planargeometry suitable for following process steps in the manufacturing flow.

Fabrication using stencil masks may be preferred over fabrication usingphotoresist masks since the photoresist mask must be cleaned off thesurface after patterning, adding a process step, while the use of astencil mask adds no cleaning step. Projection ion beam patterningoffers the same advantage.

In the case of irradiation, the passage of the ions through the sensorcan be highly constrained spatially by choice of suitable ions andenergies. As a result, the edges of the sensor can be defined to greaterprecision than is possible using currently available ion millingtechniques, irrespective of the nature of the mask used. In order tomaximize the sharpness of the pattern made by the ions, the ion speciesand energy must be selected such that the lateral scattering of ionsbeneath the mask edge is minimal while the required ion dose isachieved. Usually, this is accomplished by selecting low-Z ions, such asHe⁺, having a small projected range in the magnetic layer. In previousstudies, the parameters of ion beams for which the magnetic response issuitably modified, such as He⁺ at 30 keV, are consistent with lowlateral spreading. The small amount of lateral scattering of the ions inthe sensor film, together with the lack of physical etching, results ina sensor with essentially vertical edges rather than with the tailsfound in the current products. This significantly improves theperformance of the MR heads that incorporate these sensors.

The processes of fabricating MR sensors depicted in FIGS. 2 and 3A-3Cprovide several other advantages. The coercivity of the hard bias layermay be increased by ion exposure since ion irradiation and/orimplantation of magnetically soft thin films can cause the thin films tobecome magnetically harder. Thus in addition to defining TW of thesensor, the ion irradiation and/or implantation processes can beoptimized to induce a suitable coercivity in the film to each side ofthe sensor, providing a hard bias layer which abuts the sensor in anideal manner.

The effect of the ion irradiation on the magnetoresistance of theunmasked portions of MR sensors is described in FIG. 4. Specifically,FIG. 4A depicts a plot of the normalized magnetoresitance (ΔR/R) of theunmasked portions of a NiMn-based multilayer MR structure with a flux ofN⁺ ions at 700 keV and at a range of dose up to 10¹⁶ ions/cm². Over thisrange, the magnetoresistance ΔR/R is observed to fall to around 3% ofthe magnetoresistance of the as-produced structure. This effect alsooccurs with other spin valve and magnetic tunnel valve structuresincluding NiO.

Alternatively, controlled doping of the MR sensor with Cr, V, Al, Mo orsimilar elements also serves to greatly reduce the MR signal from theimplanted area and thus may also be used to define the TW.

The ion irradiation reduces magnetoresistance ΔR/R of the unmaskedportions of MR sensors, without substantially reducing the magneticmoment. The magnetic moment, and thus the magnetoresistance ΔR/R, of theunmasked portions may be reduced to zero by ion implantation, thusminimizing the side-reading effect of the unmasked material adjoiningthe sensor since it is no longer magnetic. An example is given below toshow the effect of the ion implantation on the magnetic moment and themagnetoresistance ΔR/R of spin valves. An exemplary spin valve with acomplete structure denoted by Si/Ru(20 Å)/NiFe(20 Å)/IrMn(80 Å)/CoFe(13Å)/NOL/CoFe(25 Å)/Cu(25 Å)/Co₉₀Fe₁₀(5 Å)/Ni₈₀Fe₂₀(40 Å)/Ru(50 Å)includes a substrate of Si, two seed layers of Ru 20 Å thick and NiFe 20Å thick, an antiferromagnetic layer of IrMn 80 Å thick, a pinned layercontaining a first layer of CoFe 13 Å thick, a nano-oxide layer NOL, anda second layer of CoFe 25 Å, a spacer layer of Cu 25 Å thick, a freelayer containing a layer of Co₉₀Fe₁₀ 25 Å thick and a layer of Ni₈₀Fe₂₀40 Å thick, and a overcoat layer of Ru 50 Å thick. This sample wasirradiated with Cr ⁺ ions at dose between 2×10¹⁴ and 2×10¹⁶ ions/cm².The Cr⁺ ion energy, 20 keV, was chosen so as to stop most of the ions inor near the free layer, as determined from a simulation of theimplantation process. The Ru overcoat layer may be diminished somewhatby milling at the high Cr⁺ doses, but this effect may be minimized byusing a low-Z element as the overcoat material. The pre-implantationmagnetoresistance ΔR/R value of the sample was about 10%. The ΔR/R valuedropped rapidly with increasing dose, and reduced essentially to zeroafter about a monolayer coverage of ions (about 3×10¹⁵ ions/cm²). Asshown in FIG. 4B, which depicts a plot of normalized magnetic moment ofthe unmasked portions of a MR multilayer structure as a function of Cr⁺ion dose, the total moment of the films dropped to zero after about 4monolayers of ions (about 2×10¹⁶ ions/cm²). The loss of magnetic momentlikely occurs because doping with Cr⁺ drives the Curie temperature belowroom temperature, transforming layers in the film from ferromagnetic toparamagnetic at room temperature. The Cr⁺ ions caused a massiveintermixing of the atoms in the multilayers, as well as the loss of someovercoat Ru to sputtering.

The sensor magnetoresistance ΔR/R can also be increased in the processof patterning TW by ion irradiation, since for some magnetoresistivemultilayer (ML) systems a small ion dose causes an increase in themagnetoresistance (MR). (e.g. D. M. Kelly et al., Increases in giantmagnetoresistance by ion irradiation in Physics Review B 50 3481(1994)). Thus, by applying a low radiation dose to the entire film toincrease the MR signal of the ML, and then inserting the mask over theelement and continuing with the irradiation until the MR of the materialsurrounding the element is diminished to zero, a sensor with enhanced MRis shaped.

The ion beam parameters will typically be selected to optimize thechange of magnetic properties of the bombarded sensor layers.Preferably, the chosen ion beam parameters also facilitate such idealsas low ion dose (short processing time), low sputtering damage to themask, economical ion beam generation (low energy, typically <100 keV),large beam area and freedom from debris. The effect of the ions on themagnetic properties may, in some multilayer sensors, depend only on theenergy loss processes as the ion passes through the ML, or differentchanges may be achieved by implantation to alter the phase structure orchemistry of the sensor layers themselves. The ion species and energywill determine whether the ion stops within the sensor (implantation) oroutside (irradiation). The important mode of ion-solid interaction maybe the ionization energy deposited at the MR interfaces by the passingion, or alternatively it might be the rate of collisional energytransfer. Furthermore, the requisite amount and form of energy transfermay be equally well provided by almost any ion species, given enoughenergy to pass through the ML. Typically, the ion energy chosen could bein the range from about 10 keV to about 1 MeV. If the ion is implantedto alter the ML composition, the ion species are predetermined, so theenergy will be chosen to lodge the ions within the ML, which may be inthe range from about 10 keV to about 1 MeV. All the ion energydeposition and stopping characteristics may be predicted by the MonteCarlo simulation software TRIM (J. P. Biersack and L. Haggmark, NuclearInstrument and Methods in Physics Research 174 257 (1980)). A personwith average skill in the art will be familiar with the choice of ionspecies and ions energies for the irradiation or implantation in atarget material typical of MR sensors using Monte Carlo software.

According to a second embodiment of the present invention, themagnetization of a MR sensor may be stabilized by using longitudinalbias for improvement of the sensor performance. FIG. 5A shows aschematic diagram of a MR sensor 500. MR sensor 500 includes a sensingelement 505 with tails 507, shaped from a continuous film using ion beammilling process in conjunction with the mask 509, located on a substrate504. The shape of the sensing element 505 and the TW are defined with anion implantation/irradiation process using mask 509. The magnetizationof sensing element 505 is conventionally stabilized by hard bias layers512 adjacent to both sides of the sensor 505. Two leads 514 are disposedover the hard bias layers 512 for transmitting electrical signals.However, the hard bias layers 512 may become very thin near the topsurface of the sensing element 505 and/or may not closely abut thesensing element 505, leading to poor sensor performance.

FIG. 5B illustrates a schematic diagram of a MR sensor 501 including asensing element 506 with the tails 508 located on a substrate 504. TheTW of the sensing element 506 is defined by introducing an extra mask510 for ion implantation/irradiation process. This mask is smaller thanthe mask used for the milling step of patterning the combined structureof sensing element 506 and tails 508. Two leads 515 overlay on the hardbias layers 513 adjacent the sensor 506, which transmit the electricalsignals. Hard bias layers 513, which are magnetically coupled to thetails 508, abut and bias the sensing element 506.

Alternatively, the magnetization of the sensor of a MR sensor may bestabilized by using an anti-parallel (AP) pinning layer as shown in FIG.5C. FIG. 5C depicts a schematic diagram of a MR sensor 503 including asensing element 519 with tails 516 located on a substrate 504. An APpinning layer including portions 517 and 521 is deposited on the sensorlayer. Portion 521 is implanted with ions of species and energy suchthat the magnetic coupling between portion 521 and underlying portion519 is destroyed, thus freeing portion 519 to behave as a sensingelement. The TW of the sensing element 519 is defined by introducingextra masks 511 on the portions 517 of the AP pinning layer forprotecting these portions 517 from the ion implantation processseparately from the milling step of patterning the MR structure. Theseportions 517 of the AP pinning layer couple with the free layer of thesensor layer in portions 516, thus these portions 516 are no longeracting like a sensor. Portions 516 and portions 517 stabilize the endsof the sensing element 519, which improves the sensing element 519performance. The masks 511 also cover leads 518 disposed adjacent theportions 516 of the sensor layer and the portions 517 of the AP pinninglayer.

Furthermore, the magnetization of a MR sensor may be stabilized by usingan in-stack antiferromagnetic (AF) layer as shown in FIGS. 5D-E. FIG. 5Ddepicts a schematic diagram of a MR sensor 520 including a sensingelement 539 with tails 521 located on a substrate 504. Two leads 527 maybe disposed adjacent to the tail 521 for transmitting electricalsignals. An in-stack AF layer 529 is disposed on the sensing element539. The TW of the sensing element 539 may be defined by introducing amask 522 on the AF layer 529 for an ion implantation/irradiation processfollowing a milling step of patterning the MR structure. The AF layer529 stabilizes the magnetization of the sensing element 539.

FIG. 5E illustrates an alternative schematic diagram of a MR sensor 540having the magnetization of the sensor stabilized by using an in-stackAF layer. MR sensor 540 includes a sensing element 523 having tails 524located on a substrate 504. An AF layer having a first portion 531covers the sensing element 523 and a second portion 530 disposed on thetails 524. The TW of the sensing element 523 may be defined byintroducing an extra mask 528 for an ion implantation/irradiationprocess separate from a milling step of patterning the MR structure. Twoleads 526 are disposed adjacent the tails 524 and the portion 530 of theAF layer for transmitting electrical signals. The portion 531 of the AFlayer stabilizes the magnetization of the sensing element 523.

MR heads incorporating MR sensors of the types depicted in FIGS. 2,3A-3C, and 5A-5E may be incorporated into disk drives. FIG. 6 depicts aschematic diagram of a disk drive 600 according to a third embodiment ofthe present invention. The disk drive 600 includes a magnetic recordingdisk 602, a MR head 604 with MR sensor 601 having features in commonwith the MR sensors described above with respect to FIGS. 2, 3A-3C, and5A-5E, an actuator 606 connected to the MR head 604, and a mechanism 608connected to the disk 602. The mechanism 608 moves the disk 602 withrespect to MR head 604. The actuator 606 moves the MR head 604 acrossthe magnetic recording disk 602 so the MR head 604 may access differentregions of magnetically recorded data on the magnetic recording disk602.

It will be clear to one skilled in the art that the above embodiment maybe altered in many ways without departing from the scope of theinvention. Accordingly, the scope of the invention should be determinedby the following claims and their legal equivalents.

1. A method for fabricating a magnetoresistive sensor comprising: a)providing a magnetoresistive structure including one or moreferromagnetic layers; b) disposing a mask between the magnetoresistivestructure and an ion source, wherein the mask covers selected portionsof the magnetorestive structure to define a sensor; and c) exposing oneor more unmasked portions of the structure to ions to substantiallyreduce or eliminate a magnetoresistance of the unmasked portionssubstantially near room temperature while leaving the magnetoresistivestructure substantially intact; allowing widths of the magnetoresistivesensor between about 5 nm and about 200 nm.
 2. The method of claim 1,wherein the ions irradiate one or more ferromagnetic layers in theunmasked portions of the magnetoresistive structure.
 3. The method ofclaim 1, wherein the ions are implanted into one or more ferromagneticlayers in the unmasked portions of the magnetoresistive structure. 4.The method of claim 1 wherein ferromagnetism of one or moreferromagnetic layers in the unmasked portions of the magnetoresistivestructure is substantially reduced or eliminated, substantially nearroom temperature.
 5. The method of claim 1 further comprising, prior toc), sputtering the unmasked portions, wherein shadowing by the maskforms one or more tails, wherein the tails are exposed to ions in c). 6.The method of claim 1, wherein the mask is a contact photolithographicresist mask.
 7. The method of claim 1, wherein the mask is a contactelectron beam resist mask.
 8. The method of claim 1, wherein the mask isa stencil mask.
 9. The method of claim 1, wherein the ions are projectedthrough a mask and focused onto the magnetoresistive structure.